Disorders of the spine occur when one or more of the individual vertebras and/or the inter-vertebral discs become abnormal either as a result of disease or injury. In these pathologic circumstances, fusion of adjacent vertebral segments may be tried to restore the function of the spine to normal, achieve stability, protect the neural structures, or to relieve the patient of discomfort.
Several spinal fixation systems exist for stabilizing the spine so that bony fusion is achieved. The majority of these fixation systems utilize fixation elements such as rods wires or plates that attach to screws threaded into the vertebral bodies or the pedicles. In particular, spinal fixation systems that attach to the pedicles (i.e., trans-pedicular) are very popular due to their stability. However, trans-pedicular fixation systems and methods require excessive muscle dissection and have been associated with harmful side effects including muscle and nerve damage in the spinal areas and increased infections, among others.
Because the outer surface of the vertebral body is typically non-planar and the structure of the vertebras is relatively complex, it is important that the fixation elements (e.g., rods, plates, wires, staples and/or screws) are properly aligned when they are inserted into the vertebras. Improper alignment may result in improper or unstable placement of the fixation element and/or disengagement of the fixation element. However, achieving and maintaining accurate positioning and guidance of these fixation elements has proven to be quite difficult in practice. Such positioning difficulties are further complicated by the fact that the alignment angle for a fixation device through one vertebral body or pair of vertebral bodies will be unique to that individual due to individual differences in the spinal curvature and anatomies.
Accordingly, there is a need for alternative fixation systems and methods that are easy to align and alleviate the above mentioned complications.